The invention relates to a method of-folding a gas bag for a vehicle occupant restraint system, a folded gas bag for a vehicle occupant restraint system and also a device for performing the method.
A restraint system for a vehicle occupant usually consists of a compressed gas source, a triggering system for this and also a gas bag which is in flow connection with the compressed gas source and after ignition of the compressed gas source can be transferred from a space-saving, folded state into an unfolded state in which it can provide a restraint effect for a vehicle occupant.
Several requirements are set for the type of folding of the gas bag. Firstly, it is to make possible as quick a transfer of the gas bag as possible from the folded into the unfolded state. Furthermore, the folding is preferably to be possible automatically. This reduces the manufacturing costs of the vehicle occupant restraint system.
The invention provides a method of folding a gas bag, which method can be carried out firstly automatically without manual steps, and secondly leads to a folded gas bag which can be unfolded in a particularly advantageous manner. The method according to the invention is intended for folding a gas bag for a vehicle occupant restraint system. This gas bag has a wall delimiting a chamber and having an inflation opening, the inflation opening having a rim. The method comprises the following steps: First, the gas bag is spread out on a base. Then, the rim of the inflation opening of the gas bag is held fixed. Thereafter, a plate is arranged parallel to the base and at a distance therefrom, so that the gas bag extends between the base and the plate. Subsequently, the chamber of the gas bag is exposed to a pressurized medium, so that the gas bag unfolds between the base and the plate. Finally, the wall of the gas bag is pressed inwards at a plurality of sites distributed over a circumference of the gas bag. In this way, a gas bag is obtained which is folded together very compactly, but which nevertheless is easy to unfold. Compared with conventional folding methods, an improvement in the unfolding time of the gas bag was able to be observed. In addition, a more uniform unfolding of the gas bag and also an improved opening behavior of a cover protecting the folded gas bag, was observed. A gas bag folded by the method according to the invention has a particularly symmetrical unfolding, whereby the positioning of the gas bag during the unfolding process is improved. Due to the particularly uniform unfolding of the gas bag, its seams and its fabric are stressed less than in gas bags which are folded by conventional methods. Owing to the improved behavior on unfolding, an impact of wall parts of the unfolding gas bag onto a vehicle occupant who is to be restrained was only observed to a distinctly lesser extent and with distinctly less energy than in gas bags which are folded by conventional methods. The method according to the invention is suitable both for gas bags on the driver""s side, i.e. for gas bags which are two-dimensional in the unpressurized initial state, and also for gas bags on the passenger""s side, which usually have a three-dimensional form in the unpressurized initial state.
According to a preferred embodiment of the invention, provision is made that the wall is pressed inwards by a plurality of fold tongues spaced apart from each other, which each engage along a line at the wall of the gas bag, so that wall flaps lying between the fold tongues are formed. Fold tongues represent a particularly simple means to press the wall of the gas bag inwards at a plurality of locations spaced apart from each other, so that the gas bag is folded together compactly.
According to a preferred embodiment of the invention, provision is made that the wall is pressed inwards in two steps, in which in the second step the wall flaps which were formed in the first step are pressed inwards. In this way, a particularly compact, folded gas bag is achieved, the wall of which nevertheless is folded very uniformly.
According to a preferred embodiment of the invention, provision is further made that the fold tongues are pressed towards the interior of the gas bag along a straight line. In this way, the method according to the invention can be carried out in a particularly simple manner.
Furthermore, provision can be made that the fold tongues are displaced in a parallel manner on being pressed towards the interior of the gas bag. This method is advantageous in particular in gas bags on the passenger side, because by means of the parallel displacement of the fold tongues, even a gas bag which has an elongated initial shape can be folded together particularly compactly.
According to a preferred embodiment of the invention, provision is further made that the wall of the gas bag is pressed in along lines which are perpendicular to the base and the plate. In this way, it is ensured that the wall of the gas bag, on unfolding, must merely move outwards substantially without changing its direction, so that the gas bag reaches its completely unfolded form.
According to a preferred embodiment of the invention, provision can be made that after the wall of the gas bag has been pressed inwardly by means of the fold tongues, the wall is pushed together by fold sliders towards the interior of the gas bag. Due to the combination of fold tongues and fold sliders, the method according to the invention can be carried out with a particularly small effort. The fold tongues which are firstly moved into the wall of the gas bag basically determine the folding pattern to be achieved. However, instead of folding together compactly the entire wall of the gas bag by means of a plurality of fold tongues, the wall can be pushed together compactly by means of less fold sliders in a simple manner.
According to a preferred embodiment of the invention, provision can be made that the wall is pushed towards the interior of the gas bag by means of four fold sliders, in which every two fold sliders lie opposite each other in pairs and in which four fold tongues are used which lie opposite each other in pairs. The use of four fold tongues and four fold sliders represents a good compromise in which, on the one hand, a reproducible folding of the gas bag is obtained, whilst, on the other hand, the effort to carry out the method is kept small.
According to a preferred embodiment of the invention, provision is made that the chamber of the gas bag is exposed to an excess pressure of less than 100000 Pa for unfolding between the base and the plate. This pressure is sufficient, on the one hand, to ensure a complete unfolding of the gas bag between the base and the plate, and, on the other hand, is not so high that the penetration of the fold tongues into the wall of the gas bag is opposed with an excessively high resistance. Preferably, provision is made that the chamber of the gas bag is exposed to a pressure of approximately 50000 Pa. This value has proved to be sufficient in tests.
According to a preferred embodiment of the invention, provision can further be made that after the gas bag has been exposed to pressure, the pressurized gas contained in the chamber of the gas bag can escape during the fold tongues or fold sliders being pressed in. In this way, the energy to be applied on pressing in the fold tongues or fold sliders into the wall of the gas bag is kept at a low value.
Furthermore, provision can be made that after folding the gas bag, a partial vacuum is applied to its chamber. In this way, the folded gas bag can be transferred into an even more compact form, whilst at the same time it is ensured that the folded gas bag, in particular after the removal of the fold elements, maintains its folded form before it is fixed elsewhere.
Preferably, provision is made that the base is arranged at a distance from the plate which corresponds approximately to the packing height of the folded gas bag. The packing height represents the height which the folded gas bag has in the interior of a mounting provided for it to be accommodated. When the distance between the base and the plate corresponds to this packing height, the gas bag which is folded by means of the fold tongues or fold sliders can be inserted directly into the mounting, without it having to be further folded or re-shaped.
The invention also provides a folded gas bag for a vehicle occupant restraint system. This gas bag has a wall delimiting a chamber and having an inflation opening, the inflation opening having a rim with an inflation opening in the wall of the gas bag. The wall of the gas bag runs in wall flaps which lie adjacent to each other. A gas bag of this type can be unfolded in a particularly advantageous manner. As regards the resulting advantages, reference is to be made to the explanations above.
According to a preferred embodiment of the folded gas bag, provision is made that the wall flaps, observed in a plane parallel to the plane of the inflation opening, run approximately radially with respect to the center of the gas bag. In this way, a particularly uniform unfolding behavior of the gas bag is produced.
According to the preferred embodiment, provision is further made that the gas bag has a substantially flat upper side and a substantially flat underside parallel thereto, the plane of the inflation opening being parallel to the plane defined by the underside. A gas bag, folded into such a shape, can be accommodated in a particularly space-saving manner in a mounting, as provided in the interior of a vehicle steering wheel or in a dashboard of a vehicle.
The invention also relates to a device for folding a gas bag, this gas bag having a wall delimiting a chamber and having an inflation opening, the inflation opening having a rim. The device comprises a base on which the gas bag to be folded can be spread out. The device further comprises a clamping device by which the rim of the inflation opening can be fixed, a plate which can be arranged parallel to the base at a determined distance therefrom, a device for introducing a pressurized medium into the gas bag chamber while the gas bag is held fixed by means of the clamping device, and a plurality of fold tongues displaceable between a position at a distance from a periphery of the gas bag which is unfolded between the base and the plate, and a position in which the wall of the gas bag is pressed inwardly towards the interior of the gas bag. The distance between the base and the plate is so selected that the gas bag which is unfolded between the base and the plate has a considerably flattened shape. With such a device, a gas bag can be folded together in a particularly simple and advantageous manner. With regard to the advantages of a gas bag folded together by means of this device, reference is to be made to the explanations above.
According to a preferred embodiment of the invention, provision is made that the fold tongues are displaceable in a straight line. A displacement of the fold tongues in a straight line can be achieved structurally in a particularly simple manner.
According to a preferred embodiment of the invention, provision can be made that the fold tongues are displaceable in a parallel manner along a part of their adjusting path. A parallel displacement of the fold tongues in fact requires a greater structural effort; this effort is, however, justified, because by means of such a device even a gas bag on the passenger side, which has an elongated shape in the spread-out state between the base and the plate, can be folded together particularly compactly.
Further features of the invention will be apparent from the sub-claims.